1. Field of the Invention
The present invention relates to a digital television, and more particularly, to an apparatus and method for improving picture quality of a digital television.
2. Background of the Related Art
Generally, unlike an interlaced scan video image, a progressive scan video image has a higher vertical resolution of about 30%, no horizontal scanning line, and no flickering, thereby being more stable and straining less a viewer""s eyes. The interlaced scan video image has a problem of easily straining the eyes of a viewer as intervals between scanning lines become larger. This problem is more apparent in large-sized screens, in which resolution is reduced.
Therefore, progressive scanning is essential in 3-tube projection televisions or projectors as well as high quality projection televisions or projectors. Furthermore, since progressive scanning improves the resolution on a temporal axis, progressive scanning is more effective in screens with actively dynamic picture images.
The aforementioned interlaced scan video image and progressive scan video image will now be described in detail.
In an interlaced scan video image, when supposing that two scanning lines A and B are vertically adjacent and that an image temporally moves from frame No.1 to frame No.2, in a static picture image, a video image has very little information on motion, thus no particular difference in information between line A and line B of frame No.1 or frame No.2 will be present.
In a dynamic picture image whereby an object is in motion, a portion of the information on line A and line B of frame No.2 may be changed from the information on line A and line B of frame No.1 or the object itself may change showing a completely different image. Thus, the overall information on line A and line B on frame No.2 is different from the overall information on line A and line B on frame No.1, which is very common when viewing television.
However, when supposing that an object moves very slightly within an identical picture image, the information on line A of frame No.2 is identical to the information on line A of frame No.1, but the information on line B of frame No.2 is different from the information of line B of frame No.1. In this case, when using an interlaced method in which the distance between line A and line B is great, pixels of the upper and lower lines A and B cannot be easily connected. Therefore, when the motion of the object is slow and small, the difference is not obvious, however, when the motion of the object is fast and large, then the resolution of the picture image is reduced and the picture image becomes unclear. In an interlaced image, especially when the video image is dynamic, a jagged edge effect, whereby a diagonal outline of an object seems jagged like a pitch wheel, may occur.
In a progressive scan video image, another scanning line is added between line A and line B of the aforementioned interlaced scan video image to improve luminance of a picture image. When the picture image is dynamic, the jagged edge effect does not occur and the pixels are more easily connected.
In other words, either a temporal axis interpolation process, which inputs information of a previous frame or a following frame, as shown in FIGS. 1A to 1C, or a perpendicular axis interpolation process, which inputs information of a lower scanning line or an upper scanning line right below or above the identical frames, as shown in FIGS. 2A and 2B, is selectively adapted.
In the temporal axis interpolation process, as shown in FIG. 3, a static image has a noticeably improved resolution and provides a much more stable video image. In the perpendicular axis interpolation process, as shown in FIG. 4, a dynamic image provides a clear video image without motion artifact noise or jagged edge effect.
Therefore, either the temporal axis interpolation process or the perpendicular axis interpolation process of the progressive scanning method is selectively used in a technique for recently improved high-quality display devices.
However, when the temporal axis interpolation process of the progressive scanning method is used, problems arise in that the jagged edge effect occurs in a dynamic image, unclear picture image also occurs, and motion artifact noise, which is typical in the progressive scanning method, increases. On the other hand, when the perpendicular axis interpolation process is used, problems arise in that indefinite outline occurs in a static picture image and a softness effect, whereby the picture image seems more or less unclear, occurs as well.
Accordingly, the present invention is directed to an apparatus and method for improving picture quality of a digital television that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus and method for improving picture quality of a digital television in which a picture image motion adaptive interpolation process is used when an interlaced picture is converted to a progressive picture, thereby providing optimal picture quality.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an apparatus for improving picture quality of a digital television includes a variable length decoder which receives compressed MPEG-2 digital video streams through a first in first out (FIFO) buffer and calculates compressed values of picture images with different compressed values, a picture image reconstructing unit which processes the digital video streams input through the variable length decoder with run length decoding, inverse scan, inverse quantization, and 8xc3x978 inverse discrete cosine transform (IDCT) to restore the video streams back to their initial states and reconstruct the video streams to a picture image with sampled values of Y/Cb/Cr, a motion compensator which extracts a motion vector from the picture image corresponding to the previous frame input through a reference buffer, extracts a motion vector from the picture output from the picture image reconstructing unit, compares a difference value between the extracted motion values with a set value to selectively apply a temporal axis interpolation process or a perpendicular axis interpolation process, and carries out progressive scanning, a storage buffer which stores picture images output from the motion compensator, and a format converter which converts the picture images stored in the storage buffer to a display format and outputs the converted picture images.
In another aspect of the present invention, a method for improving picture quality of a digital television includes the steps of restoring compressed video streams and to reconstruct a picture image, extracting a motion vector from the reconstructed picture image and extracting a motion vector from the picture image corresponding to a previous frame, calculating a difference value between the two motion vectors, applying either a temporal axis interpolation process or a perpendicular axis interpolation process according to a comparison result between the difference value and a set value and to carry out progressive scanning, and displaying the scanned picture image.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.